As the demand for integrated circuits having ever-smaller device features continues to increase, the need for improved illumination sources used for inspection of these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma light source. Laser-sustained plasma (LSP) light sources are capable of producing high-power broadband light. Laser-sustained light sources operate by focusing laser radiation into a gas volume in order to excite the gas, such as argon or xenon, into a plasma state, which is capable of emitting light. This effect is typically referred to as “pumping” the plasma.
Laser-sustained plasma illumination sources known in the art employ a pump source that emits a high-absorption laser wavelength or set of wavelengths to ignite a plasma. Laser pump wavelength is a critical parameter for igniting the plasma and achieving higher amounts of collectible power. To optimize collectible output from the plasma, wavelengths used for plasma ignition and wavelengths used to sustain the plasma are often different.
However, typical illumination pump sources are not capable of altering the wavelength, or set of wavelengths, between the ignition and sustaining phases of plasma source operation. Additionally, plasma illumination sources typically collect illumination only from the center of the plasma. Increasing power to the pump illumination source above a certain threshold results in saturation of collectible power, and only a fraction of the illumination output from the plasma is collected.
As such, it would be desirable to provide a system and method for curing the shortcomings of previous approaches such as those identified above.